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A gravitationally lensed water maser in the early Universe


Water masers1,2,3,4 are found in dense molecular clouds closely associated with supermassive black holes at the centres of active galaxies. On the basis of the understanding of the local water-maser luminosity function5, it was expected that masers at intermediate and high redshifts would be extremely rare. However, galaxies at redshifts z > 2 might be quite different from those found locally, not least because of more frequent mergers and interaction events. Here we use gravitational lensing to search for masers at higher redshifts than would otherwise be possible, and find a water maser at redshift 2.64 in the dust- and gas-rich, gravitationally lensed type-1 quasar MG J0414+0534 (refs 6–13). The isotropic luminosity is 10,000 (, solar luminosity), which is twice that of the most powerful local water maser14 and half that of the most distant maser previously known15. Using the locally determined luminosity function5, the probability of finding a maser this luminous associated with any single active galaxy is 10-6. The fact that we see such a maser in the first galaxy we observe must mean that the volume densities and luminosities of masers are higher at redshift 2.64.

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Figure 1: The 6.1-GHz water spectra of the lensed quasar MG J0414+0534.
Figure 2: The 6.1-GHz EVLA radio continuum image of MG J0414+0534.


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Our results are based on observations made using the 100-m telescope of the Max-Planck-Institut für Radioastronomie at Effelsberg and the EVLA, which is operated by the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The authors are grateful to A. Kraus and M. Claussen, who helped make these observations. J.P.McK. was supported by the European Community’s Sixth Framework Marie Curie Research Training Network ‘ANGLES’. A.B. and O.W. were supported by the Priority and Emmy-Noether-Programmes of the Deutsche Forschungsgemeinschaft, respectively.

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Correspondence to C. M. Violette Impellizzeri.

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Impellizzeri, C., McKean, J., Castangia, P. et al. A gravitationally lensed water maser in the early Universe. Nature 456, 927–929 (2008).

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